The Federal Government spends millions of dollars each year to characterize, monitor, and clean up ground- and surface-water contamination. Scientists in federal, state, and local agencies tasked with monitoring water quality must sample water quality on a frequent basis. Laboratory analysis costs often preclude collection and analysis of the large number of samples which could be used to provide detailed information on local geochemical conditions. While these are not absolutely necessary for local studies, these large numbers of samples are needed for using the data on a regional or national scale.
The U.S. Geological Survey conducted a study of the suitability of local data for regional or national monitoring programs and found that limitations in the availability of concentration data for major ions limited the usefulness of many data sets (Norris, 1990). This and other studies invalidated many data sets for national use on the basis of having too few samples and too few constituents analyzed to characterize the system of interest.
In investigating water quality using automated surface- and ground-water monitoring systems, the major ion chemistry of the systems of interest must be known (Granato and Smith, 1999; Bricker, 1998). While it is possible to take thousands of automated field measurements and hundreds of automated samples each year, the effort required for chemical titration or colorimetric methods to analyze a large number of these samples is time consuming and therefore expensive. Traditional laboratory analysis conducted in a central laboratory is expensive, and requires the additional time and expense required to ship the samples to the laboratory.
Traditional manual methods include deploying a field technician to draw samples from a well. The samples are then tested on site in accordance with established protocols, or are transported to a laboratory for analysis. However, manual methods for determining ground water quality have proven to be inherently inefficient. It is expensive to deploy field technicians to a site to retrieve test samples, and costs associated therewith only tend to increase in proportion to the number of wells tested within a given sampling site.
Personnel shortages, inclement weather, and other factors limit the frequency with which water samples can be taken manually. Typically, water samples can be tested only once or twice a month in areas having a high concentration of sites. Consequently change in water quality that take place over short periods of time, such as from surges of effluent and other contaminating influences into the water table, will often go undetected.
Improvements in assessing water quality rely on automated methods using passive techniques. In this method, a data logger controls a probe in a well to make measurements from which water quality can be determined. Automated systems have, in other monitoring applications, outperformed their manual counterparts. The use of a data logger relieves field technicians of the job of having to capture the samples to be tested. Automated systems can also be programmed to take a greater frequency of measurements as compared with measurements taken by manual methods. Since data collected by automated systems are often electronically stored, they are easier to use.
It was originally hoped that automated, self-calibrating water quality monitoring sensors could be used in an on-line water quality analysis system at each field site of interest. However, field trials indicated that, with current technology, ion selective probes would not produce consistent or reliable measurements in the field because of variations in suspended sediment, system pressure, air, and water temperature. Microbial growth and other such factors could affect measured values even with a rigorous (weekly) maintenance program.
Manual use of ion-specific probes to measure water quality have been an accepted method of water quality analysis for a number of years; Evans, 1987; Fishman and Friedman, 1989. Process flow monitoring of public and/or private water supplies and wastewater utilities, process-flow monitoring in aquaculture, and analysis procedures used in water quality laboratories has been done. However, these applications are characterized by high volume continuous operations in industrial settings which are costly to purchase and maintain. Self-calibrating industrial sensors currently available are relatively expensive (on the order of about $1,000 to $10,000 per constituent), and are limited to one constituent per unit from a known sampling matrix at a specific temperature. Also, because industrial probes are designed for process control, they are often designed to take very small subsamples and process these samples off line.
Granato et al., in U.S. Pat. No. 6,021,664, the entire contents of which are hereby incorporated by reference, disclose an automated groundwater monitoring system and method. This apparatus is designed for use on site.
Pace, U.S. Pat. No. 4,225,410, discloses an integrated miniaturized array of chemical sensors comprising ion-sensitive electrodes for concurrently analyzing a number of analytes in a fluid sample. However, this device is disposable, so there is no need to purge the system.
Tomita, in U.S. Pat. No. 5,234,568, discloses an apparatus for simultaneous measurement of a plurality of ionic concentrations using ion selective electrodes formed on the same electrode sheet.
Kurland, in U.S. Pat. No. 4,216,671, discloses a method for automatically cleaning sensing probes of water quality monitoring apparatus.
Cormier et al., in U.S. Pat. No. 5,019,238, disclose means for quantitative determination of analytes in liquids comprising units arranged seriatim to provide narrow through passageways linked to each other for determination by electrodes. Auxiliary passageways are used to allow flushing of a first sample chamber without contamination from a second sample chamber, as well as to allow measurement of a calibrating fluid.
Moss et al., in U.S. Pat. No. 5,483,164, disclose a water quality sensor apparatus for sensing a plurality of different characteristics relating to water quality. The sensors are all supported on a ceramic substrate, and signals from the sensors are fed to signal conditioning circuits which are connected to processor display and data logging units.
Brindak, in U.S. Pat. No. Re 33,468, discloses an apparatus for testing fluids for fouling which is connected in fluid flow communication to a heat transfer apparatus for in-situ testing and generation of foulant data to permit substantially simultaneous implementation of antifoulant protocol. A heating member is provided for controlled heat input, and data are simultaneously monitored and recorded.
Barcelona et al., in U.S. Pat. No. 4,803,869, disclose a portable apparatus for flow-through measurement of ground water comprising four or more electrode sensors. Electrode and other sensor malfunctions can readily be noted by calibration procedures. Gas or foreign matter is removed by dismantling, cleaning, and reassembly.
Millo, in U.S. Pat. No. 5,879,692, discloses an effluent monitoring system in which a plurality of threshold values are programmed and provides a variable and dynamic response to effluent property detecting probes for controlling a sampler device, alarm, or the like.